The transition mechanisms of tribo-electrification for self-mated metals in dry severe wear process

The effect of normal load on the tribo-electrification is investigated for 11 kinds of self-mated pure metal pairs under the dry severe wear condition in the reciprocating friction tester. Results show that with increasing normal load, the formation mechanism of wear particle varies from the micro-asperity removal, through the transition, to the particle aggregation with junction growth. Meanwhile, the polarity of tribo-electrification varies from the random, through tending to negative, to negative. This polarity is significantly influenced by the difference between the wear losses of the plate and pin specimens. A map has been established to predict the polarity of tribo-electrification according to the normal load and the surface hardness of material. During the frictional process, the wear particles have to carry an electric charge when transferred to the other surface, but this electric charge is conducted into the two bodies through contact junctions. Hence, a model is proposed to predict the magnitude of the tribo-electrification. Results show that the mean amplitude of tribo-electrification is linearly proportional to the electric resistivity and the relative wear rate, but inversely to the real contact area. This proposed model is in very good agreement with the experimental results. The dynamic real contact area is found to be the main parameter to determine the polarity of tribo-electrification. (C) 2004 Elsevier B.V. All rights reserved.